In order to taxi, an aircraft operates its engines at idle speed with occasional increases in engine speed to start motion or speed up taxi. Nearly all of the engine thrust is created by the engine fan which is driven by the engine core exhaust running through a turbine coupled via a shaft to the fan. However, the idle speed of some modern aircraft engines causes the fan to be rotated at a speed that is sufficiently high so as to cause the aircraft to travel too quickly for at least some taxi operations. Thus, pilots may be forced to routinely apply the brakes concurrent with the operation of the engines at idle speed in order to appropriately control the speed of the aircraft during taxi operations. Having to regularly utilize the brakes to control the speed of the aircraft during taxi operations increases the brake wear and leads to less productive use being made of the fuel consumed during taxi operations.
Alternatively, an aircraft may include a drive system separate from the aircraft engines in order to provide motive power to the aircraft during taxi operations. In this regard, the landing gear may include a separate drive system that may be powered during taxi operations in order to provide the motive force for the aircraft during taxi operations. However, a separate drive system to provide the motive force during taxi operations may increase the cost of the aircraft as well as the weight and corresponding fuel consumption of the aircraft. Moreover, an additional drive system dedicated to providing the motive force for the aircraft during taxi operations may include an additional set of controls that a pilot must operate in order to drive the aircraft during taxi operations, thereby adding to the complexity of the cockpit and the training requirements for a pilot.